A court heard that Ryan Giggs headbutted his ex- girlfriend and threatened to do the same to her sister.
The ex-Wales manager is on trial accused of controlling behavior as well as attacking Kate and Emma.
He said "I'll headbutt you next" after attacking her sister, according to Emma Greville.
All charges are denied by Mr. Giggs.
Giving evidence from behind a screen, Emma Greville said she saw Mr Giggs put his hands on her sister's shoulders and headbutt her.
She said Mr Giggs threatened to do the same to Emma Greville if she didn't stop screaming.
When Kate Greville told her to call the police, Mr Giggs told her to think of his daughter and career, she said.
The firm which employed Kate Greville blocked Mr Giggs' emails because of the amount he was sending her.
Kate couldn't do her work due to the email volume, according to the author.
She was giving her evidence via a video link from the United Arab Emirates.
She said that Ms Greville went to help her and her colleague set up an office in Abu Dhabi.
She said that Ms Greville was social when she first arrived.
They didn't spend as much time with her over the two years she worked there.
She appeared nervous and she was obsessed with her phone.
When she saw Ms Greville the next day, she said they had had a fight at the hotel.
She said that she was very sad.
Ms Greville had a bruise on her wrist and she asked where it came from.
She said Ms Greville said they had sex after the argument.
When she visited Ms Harvey's home in February 2020, she was asked if she saw Ms Greville.
Ms Greville said that she had been crying all night.
She claimed that Mr Giggs had been physical with her in the hotel room, and that she had been bruised on her arm.
Mr Giggs had called and messaged Ms Harvey while she was in town.
She said that some of his messages were nice, but others were rude.
She said it was like they were from different people.
She said she had met Mr. Giggs about three times.
She said she had not been present during any of the couple's arguments and had been at a wedding with the couple in Spain.
The court was told that Ms Greville was a managing partner in the UK branch of the business.